In mammals, the red blood cell is basically a small bag of hemoglobin, the protein which binds oxygen in the lungs, carries it and releases it to other tissues. A normal canine red blood cell lives 120 days and dies when it either becomes too stiff to fold itself through the tiny capillaries of the circulation (and it simply bursts trying to do so) or it cannot generate enough energy to keep itself alive.
The spleen is responsible for removing old red blood cells. The spleen possesses many tortuous, winding blood vessels where red blood cells may break if they are not supple enough to pass through. The spleen then collects the hemoglobin. Bilirubin, a pigment made from old hemoglobin, is a by-product of this process. Bilirubin is sent to the liver to be “conjugated,” a chemical process enabling the bilirubin to be excreted in bile, a digestive emulsifier secreted by the liver. Bilirubin is responsible for the brown color of feces.
Hemolysis is the destruction of red blood cells. Red blood cells may be destroyed by:
- immune-mediated pathways (in which the immune system treats red blood cells as foreign cells to be destroyed)
- the spleen’s pathways described above
- parasites that live in or or on the red blood cell (such as Mycoplasma hemofelis).
- toxins such as zinc or copper
- infections or tumors
When too many red blood cells are destroyed, the body’s mechanisms for processing hemoglobin are overwhelmed and bilirubin builds up. The patient may be obviously yellow (“jaundiced” or “icteric”) when the mucous membranes are examined. The serum may be yellow when one checks a blood sample. If the blood cells are actually being destroyed in the blood stream (rather than in the spleen), the urine will turn red or rust colored. Hemoglobin is toxic to the kidneys and kidney failure is a strong possibility.
In 1983, the US Government began minting pennies made of zinc wafers coated in copper rather than out of pure copper. As it is not uncommon for young animals to swallow pennies, zinc toxicity became recognized.
Other zinc sources include nuts, bolts, and zinc oxide based skin creams (such as diaper rash cream and sun screen). One may see a penny or other radio dense object of about the right size on a radiograph or there may be a known history of penny eating. It is important to rule out immune-mediated hemolysis as this is a common condition requiring specific treatment.
The clinical signs of zinc toxicosis include:
- red urine
- icterus (yellow mucous membranes)
- liver failure
- kidney failure
How zinc is able to produce hemolysis is not known.
If an object possibly made of zinc is seen on a radiograph, it should be removed promptly. Support then becomes crucial. Fluid therapy is important to keep circulation to the kidneys adequate and help prevent failure. Transfusion may be necessary to combat anemia and anti-nauseal therapy is warranted. Zinc is very corrosive to the stomach so medication to protect the stomach will be needed and antacids are helpful to reduce the absorption of zinc (which is enhanced by stomach acid). Research is looking at methods for binding excess zinc in the circulation similar to the way lead poisoning is treated.
Many veterinarians are unaware of this special syndrome and do not realize that pennies are far more than a simple foreign body. This is a very recently described disease and many questions are still unanswered.
Page last updated: 8/3/2011